To determine the type of metabolites, the time of generation and the metabolic pathways of transformation of the inositol phosphates (InsP) produced upon T lymphocyte activation. An early event associated with T cell receptor (TCR) / antigen (Ag) interaction is the activation of an inositol phospholipid (InsPL)-specific phospholipase C (PLC), with consequent hydrolysis of membrane phospholipids. This metabolic pathway produces a series of InsP, which may be involved in cell activation by mobilizing Ca(+2) from either endogenous or extracellular compartments. A consistent amount of evidence indicates that Ins(1,4,5)P3 metabolism may play a crucial role in the regulation of Ca(+2) metabolism. Ins(1,4,5)P3 is directly involved in Ca(+2) mobilization from intracellular stores. Studies performed in platelets and brain tissues demonstrated that Ins(1,4,5)P3 may be hydrolyzed to Ins(1,4)P2 by a specific 5-phosphomonoesterase (5PME) or phosphorylated by a 3-kinase (3K) to Ins(1,3,4,5)P4. Ins(1,4)P2 appears be deprived of biological activity, while Ins(1,3,4,5)P4 may act as a Ca(+2) mobilizer by opening certain sensitive membrane channels. The higher phosphorylated InsP5 and InsP6 may also have biological significance, perhaps acting as intercellular mediators. The present project proposes to investigate the regulation of Ins(1,4,5)P3 metabolism in human and murine T-lymphocytes in response to perturbation of the TCR. Conditions whereby different activation pathways may also be simultaneously triggered will be given special attention. This refers in particular to T cell activation by Ag in the presence of Ag-presenting, "accessory" cells with the consequent interaction with "accessory" and/or adhesion molecules. Activation of other signal transduction mechanisms, such as cAMP or cGMP by proper ligands (i.e.: prostaglandins) will also be considered regarding their effect on the generation of the InsP isomers.